Facile Construction of N-Doped Graphene Supported Hollow PtAg

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Facile construction of N-doped graphene supported hollow PtAg nanodendrites as highly efficient electrocatalysts towards formic acid oxidation reaction Hui Xu, Bo Yan, Shumin Li, Jin Wang, Caiqin Wang, Jun Guo, and Yukou Du ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.7b02935 • Publication Date (Web): 30 Nov 2017 Downloaded from http://pubs.acs.org on December 6, 2017

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ACS Sustainable Chemistry & Engineering

Facile construction of N-doped graphene supported hollow PtAg nanodendrites as highly efficient electrocatalysts towards formic acid oxidation reaction Hui Xua, Bo Yana, Shumin Lia, Jin Wanga, Caiqin Wangb, Jun Guoc, Yukou Du *a a

College of Chemistry, Chemical Engineering and Materials Science, Soochow University, 199 Renai Road, Suzhou 215123, PR China b

Chemistry Department, University of Toronto, Toronto M5S3H4, RP Canada. c

Testing & Analysis Center, Soochow University, 199 Renai Road, Jiangsu 215123, China

* Corresponding author: Tel: 86-512-65880089, Fax: 86-512-65880089; E-mail: [email protected] (Y. Du).

ABSTRACT

The lack of cost-efficient catalysts for the electrooxidation of fuel in the anodic electrode has been the major barrier for the practical large-scale commercial application, and hence needs to be optimized. Tuning the morphologies and structures of Pt-based bimetallic nanostructure plays a key role in controlling its interaction with reactants, and thus affects its electrocatalytic efficiency. In this regard, endowing the nanocatalysts with both of high surface active areas and controlled facets through modifying their surface compositions and morphologies can significantly enhance their electrocatalytic performances. To this end, we herein demonstrate a

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facile wet-chemical method to successfully construct the N-doped graphene supported hollow PtAg nanodendrites under the assistance of ultrasonic process. More importantly, the resulted Ndoped graphene supported hollow PtAg nanodendrites show high performance for the electrooxidation of formic acid with the mass and specific activities of 1258.5 mA mg-1 and 6.14 mA cm-2, 3.77 and 1.57-fold enhancements than those of commercial Pt/C, respectively. It is believed that the as-prepared nanomaterials can be well-applied to serve as the highly efficient anode electrocatalysts for the commercial application of fuel cells and beyond. Keywords: N-doped graphene; Hollow PtAg nanodendrites; Formic acid electrooxidation; Fuel cells; Highly efficient; Long-term stability INTRODUCTION Direct fuel cells represent the promising renewable energy conversion and storage technology in recent years.1-2 Among many direct fuel cells, the direct formic acid fuel cells (DFAFCs), with the features of nontoxic and nonflammable properties, less crossover flux but ultrahigh energy density, environmental benignity, can efficiently convert the chemical energy into electric energy.3-5 Although of these favorable terms, the lack of cost-efficient electrocatalysts still limited their commercial development. As the central components of fuel cell device, catalysts played the key roles in dictating their ultimate electrochemical performances.6 Up till now, Pt and Pt-based nanomaterials have been regarded as the highly efficient electrocatalysts for the oxidation reaction of formic acid in the DFAFCs.7 However, both of the sacredly natural abundance

and

ultrahigh

cost

have

seriously

limited

their

practical

large-scale

commercialization.8


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The most successful approach to boost the electrocatalytic performances of catalysts is alloying Pt with some other transition metals to form the PtM alloy catalysts, where M has been Au, Ag, Cu and so on.9-12 Among these catalysts ligands, Ag, emerged as the desirable catalyst ligand, have drew plenty of attentions due to the facts that the introduction of Ag can not only simultaneously modify the electronic structure but also boost the activation of surface active sites.13-14 Besides, Ag also displays exceptional anti-poisoning property during the electrooxidation of liquid fuel.15-17 In addition, precisely tuning and optimizing the surface structure through adjusting the morphologies of electrocatalysts is believed to be an effective approach to enhance their electrocatalytic performances.18-19 Thanks to their unique physiochemical properties such as high surface to volume ratio, large void space, 3D catalytic surfaces and high utilization of precious metals,20 the hollow dendritic structure has attracted extensive notices for it can not only harvest the costly materials and supply the surface active sites available for organic molecules, but also facilitate the charge transfer, which thus can greatly improve their electrocatalytic performances.21-22 Apart from these, the introduction of catalyst supports such as carbon materials (carbon black, carbon nanotubes, graphene), conductive polymers and metal oxides, with the properties of high surface area, good electric conductivity,

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strong affinity and chemical and thermal stability

have also been regarded as an efficient tactic to enhance their electrocatalytic activity.26 Among various supports, graphene, an ultrathin and rigid two-dimensional (2D) single-layer sheet of hexagonal carbon nanosheet, emerged as a newly generated catalyst support in fuel cells due to its relatively high electron mobility, very high theoretical surface area, good chemical and environmental stability together with superior conductive effect.27-29 Additionally, incorporating


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the graphene with some heteroatoms such as sulfur, nitrogen, phosphorus, boron to form graphene hybrids with synergistic effects can well modify their physiochemical properties. Among these dopants, nitrogen (N) is undoubtedly deemed to be the most excellent element used for doped materials, for which can not only assist in dispersing the catalysts nanoparticles, but also modulate the electrochemical properties of graphene to provide multidirectional electron transfer route.30-32 Besides, the graphene embedded with nitrogen atoms was also found to be favorable for supplying with more active sites for the electrooxidation of formic acid molecules,33 as well as greatly strengthening the connections between metal nanoparticles and graphene, which are ultimately beneficial for substantial improvement of electrocatalytic activity and durability.34-36 An integration of efficient catalysts supports, available surface areas, synergistic effects and unique hollow structure thus seems naturally to be extremely beneficial for the facile design and fabrication of highly efficient Pt-based catalysts with the maximized utilization of Pt.37 Based upon these analyses, we herein demonstrated a facile combined seed mediated and galvanic replacement method to successfully synthesize the bimetallic PtAg nanocatalysts with the fascinating hollow nanodendritic structures. Impressively, by virtue of the large accessible surface active areas, synergistic and electronic effect, the resulting PtAg nanocatalysts show superior electrocatalytic performances for the electrooxidation of formic acid with the mass and specific activities of 1258.5 mA mg-1 and 6.14 mA cm-2, 3.77 and 1.57 times higher than those of commercial Pt/C, respectively. EXPERIMENTAL SECTION Preparation of Ag seeds


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In this work, the first step is to synthesize the Ag seeds, which can be easily prepared according to the method described by previously reported work.38 In the typical synthesis, 23.8 mg tannic acid and 83.2 mg sodium citrate were simultaneously added into a three-neck flask containing 20 mL DI water. And the reaction system was then transferred to an oil bath with the temperature of 105 °C under rapid magnetic stirring. After that, 2 mL of AgNO3 (10 mM) solution was injected to the above mixture dropwise. After continuous reaction for 10 min, the color of the solution turned into dark brown, suggesting the reduction of Ag ions. Finally, the resulting Ag seed were re-dispersed in 10 mL DI water for further use. Preparation of N-doped graphene supported PtAg hollow nanodendrites In the standard syntheses of N-doped graphene supported PtAg hollow nanodendrites, 1.4 mL H2PtCl6 (7.7 mM) was firstly injected into 10 mL aqueous solution in a glass vial, which contained 10 mg hexadecyltrimethylammonium chloride (CTAC). After vigorous stirring for 10 min, 1 mL of 0.5 mg mL-1 N-doped graphene (nitrogen, 3.0 wt%～5.0 wt%, purchased from the Nanjing XFNANO Materials Tech Co., Ltd.) solution (dissolved in N, N-dimethylformamide solution) was dropped into above solution with rapid stirring. After that, 4 mL of ascorbic acid (10 mg) was then added dropwise to the above solution to serve as the reducing agent. After continuous reaction for 3 min, 5 mL of freshly-prepared Ag seeds were dropped to this aqueous solution. After the aqueous solution has been violently shaken and capped, and then ultrasonic at ambient temperature for another 2 h. Considering the standard reduction potential of Ag+/Ag is much lower than that of PtCl62-/Pt, it is reasonable to believe that the galvanic displacement reaction contributes to the formation of hollow nanostructure by serving the above Ag seeds as template. The galvanic replacement reaction between Ag and H2PtCl6 is as follow: 4 Ag + H2PtCl6 → Pt + 4 AgCl + 2 HCl

(1)


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And the following addition of ascorbic acid (AA, reducing agent) in this work can co-reduce PtCl62- and Ag+ ions followed by their co-deposition on the Ag seeds to form the hollow nanodendrities, and the Ag+ ions originate from the galvanic replacement between Ag and PtCl62-. Generally speaking, the freshly prepared Ag seeds can firstly react with Pt (IV) ions and form some Pt atoms, which then deposited on the surface of Ag seeds to yield some pinholes. After that, hollow nanostructures were formed due to the dissolution of Ag from the pinholes and continuous deposition of Pt atoms onto the surface. After the successive dissolution of Ag seeds and continuous deposition of Pt for 2 hours with the assistance of sonicate, finally formed the hollow PtAg nanodendrites. For comparison, the other two types of PtAg/NG catalysts with different compositions can also be prepared by tuning the amounts of Ag seeds, while keep the conditions unchanged. The syntheses of PtAg are same as the preparation of PtAg/NG nanocatalysts but in the absence of N-doped graphene. Characterizations The representative TEM images of these electrocatalysts were employed to analyze the morphological and structural properties of the resulted products. The specific structures and crystal properties of the samples were evaluated by the X-ray diffraction (XRD) using Cu Kα as the radiation source (λ = 1.54056 Å). In addition, we have also employed the X-ray photoelectron spectroscopy (XPS) operated on a VG Scientific ESCALab 220XL electron spectrometer using 300 W Al Kα radiation to investigate the compositions and elemental valences of the samples. Electrochemical measurements


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In this work, we have employed the cyclic voltammetry (CV) to investigate their electrocatalytic performances, which conducted at the potential ranging from -0.3 to 0.9 V with the sweeping rate of 50 mV/s. More importantly, every time before examination, the glassy carbon electrode (GCE) needed to be polished with alumina powder and then rinsed with doubly deionized water and ethanol for several times. The theoretical value of Pt loading on the surface of GCE was calculated to be 2.1 µg, which is close to the results from the ICP-AES. After that, 3 µL of nafion (0.05%) was employed to cover on the surface of catalysts power and then dried before measurement for avoiding the dissolution of the catalysts ink. Besides, the measurements of chronoamperometry (CA) and successive CVs of 500 cycles have also been conducted for investigating their long-term durability. RESULTS AND DISCUSSION Physicochemical characterizations A typical wet-chemical method under the assistance of ultrasonic process has been adopted to synthesize such fascinating hollow PtAg nanocatalysts with the dendrite-like shell. The morphological and structural features were firstly characterized via TEM. From the Fig.1, it is clearly found that the products consisted of the uniform hollow nanoparticles with the dendritelike shell, the nanoparticles were highly dispersed with an average size of 53.8 ± 5.9 nm (seen in Fig.1D). It has been well demonstrated that CTAC played a significant role in affecting the morphology of the nanocatalysts. In this regard, we herein prepared the PtAg nanoparticles in the absence of CTAC, while kept the other conditions the same. From the Fig.S1 (Supporting Information), we can’t observe any nanocatalysts with unique morphology but just some bulk counterpart, indicating that CTAC was crucial for the successful syntheses of such unique hollow PtAg nanodendrties.


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Fig.1 (A-C) Representative TEM images of hollow Pt1Ag1 nanodendrites with different magnifications and (D) their size distributions calculated from the 100 randomly selected particles. In this work, we have also selected the N-doped graphene as the ideal catalysts support to assist in dispersing and anchoring the nanoparticles.39 Fig.2 displayed the N-doped graphene


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supported hollow PtAg nanodendrites with the different magnifications obtained under the assistance of ultrasonic.36 As observed, the hollow PtAg nanodendrites were well-dispersed on the surface of NG and interconnected with each other, which would benefit for supplying with massive surface active areas and ultimately leading to the great enhancements of electrocatalytic activity.40

Fig.2 Representative (A and B) TEM, (C) HR-TEM and (D) EDS-mapping images of Pt1Ag1/NG. Impressively, Fig.3 showed the representative TEM images of the other two types of hollow PtAg nanodendrites with different compositions. As seen, same as Pt1Ag1/NG, both of


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Pt1Ag2/NG and Pt2Ag1/NG nanocrystals also displayed the typical hollow dendrite-like structure, which also dispersed uniformly on the surface of N-doped graphene, indicating that this strategy can be well applied to synthesize these fascinating electrocatalysts at large scale regardless of the variations of atomic ratios.41-42 Based upon these characterizations, we may easily find that such N-doped graphene supported PtAg hollow nanodendrites can be well applied as the ideal anodic electrocatalysts for the practical large-scale production of fuel cells.43


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Fig.3 Representative TEM images of (A and C) Pt1Ag2/NG and (B and D) Pt2Ag1/NG with different magnifications.

Fig.4 XRD patterns of Pt, Pt1Ag1, Pt2Ag1/NG, Pt1Ag1/NG and Pt1Ag2/NG. On the sake of investigating their unique phase structures, the X-ray diffraction (XRD) is also employed. As it can be observed in Fig.4, the four typical peaks presented at the 2θ value of about 39.1, 45.7, 66.8 and 79.9 could be attributed to the (111), (200), (220) and (311) lattice planes of the fcc crystalline Pt [JCPDS no. 04-0802]

44

, while the diffraction peak presented at


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the 2θ degree of around 24 could be ascribed to the typical C (002) peak of N-doped graphene, indicating that such hollow PtAg nanodendrites have been successfully deposited on the surface of N-doped graphene.45 Specifically, in comparison with pure Pt, all the PtAg/NG shifted to the lower angles. More importantly, with the incensement of Ag content, the PtAg/NG shifted to a much lower angle, suggesting the formation of alloy phase in such PtAg/NG sample.46 Moreover, on the purpose of understanding the compositions and elemental valences of such Pt1Ag1/NG, the XPS measurements were employed to identify the states of the C, N, Pt and Ag in bulk materials and the typical results were shown in Fig.5. As is displayed in Fig.5A, the typical peak appeared at about 284.4 eV can be ascribed to the C−C bonds with sp2/sp3 hybrid carbon in the C 1s spectrum of NG, while the other four peaks located at a little higher binding energy (B.E.) can be reasonably corresponding to the following carbon functional groups: C–C (284.7eV), C–N (285.6 eV), C–O (286.7 eV), C=O (287.4 eV) and O–C=O (289.6 eV). As seen in Fig.5B, the typical N 1s spectrum can be deconvoluted into three types of nitrogen, which are associated with amino-type N, graphitic-type N and pyridinictype N, respectively. Fig.5C displayed the representative XPS spectra of Pt 4f, where the peaks at the B.E. of 71.7 and 74.6 eV are assigned to the Pt 4f 7/2 and 4f 5/2 states, respectively.47 Apparently, the XPS of Pt 4f7/2 in the Pt1Ag1/NG shifted positively to a larger angle in comparison with that of Pt 4f

7/2

in Pt/C

(Fig.5E), indicating the changes in the electronic structure, which may be attributed to the occurrence of charge transfer between Pt and Ag. As seen in Fig.5F, the B.E. of Ag 3d

5/2

in

Pt1Ag1 NCs exhibited an obviously slight shift to a lower B.E. when compared with the pure Ag (368.3 eV), further suggesting the occurrences of charge transfer between Pt and Ag. More importantly, both of the metallic states of Pt and Ag (Fig.5D) are the dominated states in such N-


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doped graphene supported Pt1Ag1 hollow dendrites, indicating the complete reduction of H2PtCl6 and AgNO3.


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Fig.5 XPS spectra of (A) C 1s, (B) N 1s, (C) Pt 4f and (D) Ag 3d in Pt1Ag1/NG. (E) Pt 4f in Pt/C and (F) Ag 3d in Ag/C Electrochemical measurement Because of such fascinating hollow nanodendrites structure, as well as the introduction of ideal N-doped graphene, the resulting hollow PtAg/NG were highly expected to display outstandingly excellent electrocatalytic performances for the electrooxidation of liquid fuel. To this end, we herein selected the formic acid oxidation reaction (FAOR) as the model reaction system to evaluate their electrocatalytic performances.48-49 The CV of all the electocatalysts were firstly conducted in the solution of 0.5 M H2SO4 at the potential ranging from -0.3 to 0.9 V. From the Fig.6A and Fig.6B, we could see that the peaks appeared around the potential of 0 and -0.2 V can be assigned to the typical peaks of hydrogen adsorption/desorption, while the peaks emerged at the potential around 0.75 (forward) and 0.55 V (backward) can be ascribed to the oxidation/reduction of Pt, respectively.50 The electrochemical active surface area (ECSA) is a significant parameter to evaluate their electrocatalytic properties, which can be estimated by the equation as follow 51: ECSA = QH/ 0.21× Ptm, Where 0.21 (mC cm−2) is the necessary charge to oxidize a monolayer of hydrogen on the smooth surface of Pt, Ptm is associated with the mass of Pt loading on the surface of working electrode and the QH (mC cm−2) is associated with the hydrogen adsorption/desorption areas. And the calculated ECSA values obey the order as follow: Pt/C (8.5 m2 g-1) < Pt1Ag1 (13.2 m2 g-1) < Pt2Ag1/NG (15.1 m2 g-1) < Pt1Ag2/NG (17.7 m2 g-1) < Pt1Ag1/NG (20.5 m2 g-1), indicating that such Pt1Ag1/NG possessed the highest electrochemically surface active sites after the introduction of N-doped graphene. After such activate process, the typical CV measurements were then operated in the solution containing 0.5 M HCOOH and 0.5 M H2SO4 at the scanning rate of 50 mV s-1. From the Fig.6C,


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the forward anodic peak currents represent the electrocatalytic activities of these catalysts. For a detailed comparison, the current densities of these electrocatalysts were normalized with the mass of Pt loading on the surface of the GCE. Fig.6D recorded the calculated mass and specific activities of these five types of electrocatalysts. As observed, the Pt1Ag1/NG displayed the mass (normalized with the mass of Pt loading on the surface of GCE) / specific activity (normalized with the ECSA value) of 1258.5 mA mg-1 and 6.14 mA cm-2, 3.77 and 1.57-fold enhancements than those of commercial Pt/C (333.8 mA mg-1 and 3.92 mA cm-2), indicating that the formation of PtAg alloy and the successful introduction of NG support can tremendously enhance the electrocatalytic performances of single Pt catalysts.52 Moreover, both of the Pt1Ag2/NG and Pt2Ag1/NG also displayed the greatly enhanced mass / specific activity of 938.3 mA mg-1 / 5.32 mA cm-2 and 671.3.3 mA mg-1 / 5.34 mA cm-2, respectively, much higher than those of Pt1Ag1 (639.7 mA mg-1 / 4.85 mA cm-2). It has been proposed that the introduction of Ag atoms can greatly raise the 5d-orbitals vacancy of Pt and reduce the back-donation of 5d electrons to CO. All of these are favorable for weakening the interaction between Pt and COads and leading to the enhancement of catalytic capability. In addition, the introduction of Ag can also simultaneously facilitate the intermediate oxidation and cleavage of C-C bonds, as well as boost the activation of surface active sites of Pt. Therefore, Ag atoms played the significant role in enhancing the electocatalytic performances towards formic acid electrooxidation.53 All of these conclusions can also forcefully illustrate that the synergistic effect and electron transfer between Ag and Pt, as well as the introduction of NG support are beneficial for significantly enhancing the electrocatalytic performances.54


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Fig.6 The CV of (A) commercial Pt/C, Pt1Ag1 and Pt1Ag1/NG, (B) Pt2Ag1/NG, Pt1Ag1/NG and Pt1Ag2/NG operated in 0.5 M H2SO4. (C) The CV curves of commercial Pt/C, Pt1Ag1, Pt2Ag1/NG, Pt1Ag1/NG and Pt1Ag2/NG conducted in the solution containing 0.5 M H2SO4 and 0.5 M HCOOH and (D) their calculated mass and specific activities. Apart from these, the long-term durability is also a crucial parameter used to evaluate their electrocatalytic properties. Inspired by this, the chronoamperometry measurement conducted at the fixed potential of 0.4 V was also employed to investigate their durability. As seen in Fig.7A, although the peak current densities of all electrocatalysts decayed rapidly in the incipient stage, the Pt1Ag1/NG displayed the slowest rate of descent and retained the highest mass activity


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among these catalysts, indicating its superior durability, which further confirm their excellent electrocatalytic performances.55 For making a detailed comparison, the retained mass activities and normalized current densities of these electrocatalysts were also recorded in Fig.7B. As seen, the Pt1Ag1/NG possessed the highest retained mass activity and normalized current density of 119.3 mA mg-1 and 9.4 %, much higher than those of Pt/C (7.7 mA mg-1 and 2.3 %), Pt1Ag1 (20.1 mA mg-1 and 3.14 %), Pt2Ag1/NG (28.8 mA mg-1 and 3.78 %) and Pt1Ag2/NG (938.3 mA mg-1 and 5.32 %). Besides, the successive CVs of 500 cycles were also operated to investigate their long-term stability. As observed in Fig.S2, Similar with the CA curves, the normalized peak current densities of all these electrocatalysts decayed rapidly with the increases of cycle numbers, while the Pt1Ag1/NG kept the highest retained normalized current among these electrocatalysts.56 Fig.7C and Fig.7D summarized the retained mass activities and normalized current densities of these electrocatalysts after successive CVs of 500 cycles. As seen, the Pt1Ag1/NG displayed the highest retained mass activity and normalized current of 388.9 mA mg-1 and 30.9 %, much higher than those of the commercial Pt/C (29.4 mA mg-1 and 8.8 %) and the other electrocatalysts. Based upon these evaluations, we may easily summarize that the such Pt1Ag1/NG with the hollow dendrites-like structure possessed the extremely superior electrocatalytic performances towards FAOR when compared with other catalysts, suggesting it can be well-applied to serve as the highly efficient electrocatalysts for DFAFCs and beyond.


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Fig.7 CA curves of commercial Pt/C, Pt1Ag1, Pt2Ag1/NG, Pt1Ag1/NG and Pt1Ag2/NG nanocatalysts operated at the fixed potential of 0.4 V for 3600 s, and (B) their calculated mass activities and normalized current after 3600s. (C) Successive CVs of 500 cycles of these electrocatalysts and (D) their calculated mass activities and normalized current densities after 500 cycles. In order to fully understand the specific electrochemical reaction process, we herein conducted the electrochemical impedance spectroscopy (EIS) for these five catalysts at the potential of 0.35 V.57 As it can be observed in Fig.8, the order of the diameter of the impedance arc (DIA) of these electrocatalysts displayed as follows: Pt/C > Pt1Ag1 > Pt2Ag1/NG > Pt1Ag2/NG > Pt1Ag1/NG.


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Apparently, the resulting Pt1Ag1/NG possessed the smallest DIA, indicating its smallest chargetransfer resistance but best electrical conductivity for the FAOR. 58 In all, the newly-generated N-doped graphene supported PtAg hollow nanodendrites exhibited outstandingly superior electrocatalytic performances towards FAOR when compared with PtAg nanocrystals and commercial Pt/C catalysts. The greatly enhanced electrocatalytic performances can mainly be ascribed to the following aspects: (1) The inherent properties of such hollow nanodendrites structure with much higher surface-to-volume ratio but lower material density can render such porous PtAg/NG nanocrystal an ideal structure with both of enhanced catalytic activity and improved long-term stability.59 (2) The synergistic and electronic effects evolved from Pt, Ag and N also be conductive to boosting the charge transfer and leading to the enhancements of catalytic performances.60-62 (3) The introduction of N-doped graphene is favorable for adjusting the electron transport of the substrate, which, in turn, strengthening the interaction between the PtAg nanoparticles and the substrate.


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Fig.8 Nyquist plots of FAOR on commercial Pt/C, Pt1Ag1, Pt2Ag1/NG, Pt1Ag1/NG and Pt1Ag2/NG nanocatalysts conducted at the fixed potential of 0.35 V. CONCLUSIONS In summary, a novel class of N-doped graphene supported PtAg hollow nanodendrites have been fabricated through the typical wet-chemical method with the assistance of sonicate process. The as-obtained hollow PtAg nanodendrites can disperse uniformly on the surface of N-doped graphene. Owing to the large accessible surface active sites, synergistic and electronic effects, the as-obtained N-doped graphene supported hollow PtAg nanodendrites possessed great


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enhancements of electrocatalytic activity towards FAOR with the mass and specific activities of 1258.5 mA mg-1 and 6.14 mA cm-2, much higher than those of commercial Pt/C and PtAg nanocatalysts. In addition, the successive CVs of 500 cycles and CA measurements have demonstrated their outstandingly high long-term stability. All of these results further demonstrated it as an advanced class of Pt-based nanocatalysts with high performance and improved utilization efficiency of Pt for potentially practical applications in DFAFCs. Our tremendous efforts in this work have demonstrated a facile method for the creation of ultrafine catalysts with outstanding catalytic performances, which will greatly prompt the commercial development of fuel cells and beyond. ASSOCIATED CONTENT Supporting Information Fig.S1 Representative TEM images of PtAg nanocrystals prepared in the absence of CTAC with different magnifications, while keep other conditions unchanged.

Fig.S2 CV (1st, 100th, 200th, 300th, 400th and 500th) curves of (A) Pt1Ag1/NG, (B) Pt1Ag1 and (C) commercial Pt/C operated in the solution containing 1 M KOH and 1 M EG at the scanning rate of 500 mV/s.

AUTHOR INFORMATION Corresponding Author Tel: 86-512-65880089, Fax: 86-512-65880089; E-mail: [email protected] (Y. Du). Author Contributions


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The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. ‡These authors contributed equally. (match statement to author names with a symbol) Notes Any additional relevant notes should be placed here. ACKNOWLEDGMENT This work was supported by the National Natural Science Foundation of China (Grant No. 51373111), the Suzhou Industry (SYG201636), the project of scientific and technologic infrastructure of Suzhou (SZS201708), the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD) and the State and Local Joint Engineering Laboratory for Novel Functional Polymeric Materials. REFERENCES 1.

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Table of Content The N-doped graphene supported hollow PtAg nnaodendrites catalysts possess superior electrocatalytic performances towards formic acid oxidation due to the modified morphology, demonstrating an excellent electrocatalysts for fuel cells.


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Facile Construction of N-Doped Graphene Supported Hollow PtAg

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